Safracins, a family of new compounds with a potent broad-spectrum antibacterial activity, were discovered in a culture broth of Pseudomonas sp. Safracin occurs in two Pseudomonas sp. strains, Pseudomonas fluorescens A2-2 isolated from a soil sample collected in Tagawagun, Fukuoka, Japan (Ikeda et al. J. Antibiotics 1983, 36,1279-1283; WO 82 00146 and JP 58113192) and Pseudomonas fluorescens SC 12695 isolated from water samples taken from the Raritan-Delaware Canal, near New Jersey (Meyers et al. J. Antibiot. 1983, 36(2), 190-193). Safracins A and B, produced by Pseudomonas fluorescens A2-2, have been examined against different tumor cell lines and has been found to possess antitumor activity in addition to antibacterial activity.
Due to the structural similarities between safracin B and ET-743 safracin offers the possibility of hemi-synthesis of the highly promising potent new antitumor agent ET-743, isolated from the marine tunicate Ecteinascidia turbinata and which is currently in Phase II clinical trials in Europe and the United States. A hemisynthesis of ET-743 has been achieved starting from safracin B (Cuevas et al. Organic Lett. 2000, 10, 2545-2548; WO 00 69862 and WO 01 87895).
As an alternative of making safracins or its structural analogs by chemical synthesis, manipulating genes of governing secondary metabolism offer a promising alternative and allows for preparation of these compounds biosynthetically. Additionally, safracin structure offers exciting possibilities for combinatorial biosynthesis.
In view of the complex structure of the safracins and the limitations in their obtention from Pseudomonas fluorescens A2-2, it would be highly desirable to understand the genetic basis of their synthesis in order to create the means to influence them in a targeted manner. This could increase the amounts of safracins being produced, because natural production strains generally yield only low concentrations of the secondary metabolites that are of interest. It could also allow the production of safracins in hosts that otherwise do not produce these compounds. Additionally, the genetic manipulation could be used for combinatorial creation of novel safracin analogs that could exhibit improved properties and that could be used in the hemi-synthesis of new ecteinascidins compounds.
However, the success of a biosynthetic approach depends critically on the availability of novel genetic systems and on genes encoding novel enzyme activities. Elucidation of the safracin gene cluster contributes to the general field of combinatorial biosynthesis by expanding the repertoire of genes uniquely associated with safracin biosynthesis, leading to the possibility of making novel precursors and safracins via combinatorial biosynthesis.